The operation of printing with calibrated colors is computationally expensive. Transformation from the input (e.g. computer display) color space to the output (e.g. native printer) color space frequently involves 3-D or 4-D, real number interpolation. Every color that is used on the printed page must be separately transformed. This is a significant problem when printing continuous tone images where virtually every pixel represents a different color. Color transformations can represent a significant portion of the total time spent processing the printed page. A method that reduces the number of color transformations involved in the printing work flow would be welcome.
Standard graphic arts printing workflow involves a host-based application working in a calibrated color space (e.g. ink simulation), a printer driver and a color printer. The application specifies and displays its colors in a calibrated color space. In the case of a PCL printer driver the driver must convert the application color space into a color space understood by the PCL page description language. PCL-5c understands only the (semi-calibrated) sRGB color space and (uncalibrated) CMY. The converted page description is then passed to the printer, where the firmware transforms the page description one or more times into the native printer color space.
Some PostScript printer drivers work essentially the same way except that PostScript may accept the calibrated application color space (e.g. CIE) directly, possibly avoiding one color transformation in the printer driver. Unfortunately PostScript uses the XYZ calibrated color space internally and thus must first convert the page description into the XYZ color space before converting it back into the printer device color space. Thus PostScript, as with PCL, uses a minimum of two color space conversions when printing calibrated colors.
Real work flows are frequently more complex than described above. Additional color transformations may be required.